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std::is_sorted

From cppreference.com
< cpp‎ | algorithm
 
 
Algorithm library
Execution policies (C++17)
Non-modifying sequence operations
(C++11)(C++11)(C++11)
(C++17)
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
is_sorted
(C++11)
Binary search operations
Set operations (on sorted ranges)
Heap operations
(C++11)
Minimum/maximum operations
(C++11)
(C++17)

Permutations
Numeric operations
C library
 
Defined in header <algorithm>
template< class ForwardIt >
bool is_sorted( ForwardIt first, ForwardIt last );
(1) (since C++11)
template< class ExecutionPolicy, class ForwardIt >
bool is_sorted( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last );
(2) (since C++17)
template< class ForwardIt, class Compare >
bool is_sorted( ForwardIt first, ForwardIt last, Compare comp );
(3) (since C++11)
template< class ExecutionPolicy, class ForwardIt, class Compare >
bool is_sorted( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Compare comp );
(4) (since C++17)

Checks if the elements in range [first, last) are sorted in non-descending order.

1) Elements are compared using operator<.
3) Elements are compared using the given binary comparison function comp.
2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Contents

[edit] Parameters

first, last - the range of elements to examine
policy - the execution policy to use. See execution policy for details.
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than (i.e. is ordered before) the second.

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function object must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
-
ForwardIt must meet the requirements of ForwardIterator.

[edit] Return value

true if the elements in the range are sorted in ascending order

[edit] Complexity

linear in the distance between first and last

[edit] Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

  • If execution of a function invoked as part of the algorithm throws an exception, std::terminate is called.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] Possible implementation

First version
template<class ForwardIt>
bool is_sorted(ForwardIt first, ForwardIt last)
{
    return std::is_sorted_until(first, last) == last;
}
Second version
template<class ForwardIt, class Compare>
bool is_sorted(ForwardIt first, ForwardIt last, Compare comp)
{
    return std::is_sorted_until(first, last, comp) == last;
}

[edit] Example

#include <iostream>
#include <algorithm>
 
int main() 
{
    const int N = 5;
    int digits[N] = {3, 1, 4, 1, 5};
 
    for (auto i : digits) std::cout << i << ' ';
    std::cout << ": is_sorted: " << std::is_sorted(digits, digits+N) << '\n';
 
    std::sort(digits, digits+N);
 
    for (auto i : digits) std::cout << i << ' ';
    std::cout << ": is_sorted: " << std::is_sorted(digits, digits+N) << '\n';
}

Output:

3 1 4 1 5 : is_sorted: 0
1 1 3 4 5 : is_sorted: 1

[edit] See also

finds the largest sorted subrange
(function template) [edit]
parallelized version of std::is_sorted
(function template) [edit]